The invention relates to an exhaust system of a multi-cylinder internal-combustion engine, the exhaust gases of which are guided by means of a collector approximately centrically to a housing which has catalysts at opposite ends, all exhaust gas being lead out to the open air downstream of the catalysts.
In the German Patent Document DE- 2 452 675, an exhaust system is disclosed in which the exhaust gases flow by way of a collector into an interior housing surrounded by an exterior housing. In this case, the exhaust gases first reach an afterburning chamber in a central manner and are guided from there as separate flows through two catalysts arranged on opposite ends of the interior housing into the exterior housing, in which the exhaust gas flows are mixed again and reach the open air by way of a common exhaust.
From the German Patent Document DE- 21 17 771, an exhaust system is known in which pipe sections, which extend from one cylinder bank respectively of the internal-combustion engine into a muffler, have a perforated construction inside this muffler. The German Patent Document DE-39 30 380 shows an exhaust system of a multi-cylinder internal-combustion engine in which starting catalysts are connected into the exhaust pipes which are connected directly to the cylinder head, which starting catalysts have a central duct, which can be closed by a flap, and a ring duct which surrounds it and contains the catalyst material.
The invention is based on the object of providing an exhaust system for an internal-combustion engine which, while its arrangement is space-saving, has a low exhaust back pressure and achieves an optimal exhaust emission control.
This object is achieved by means of an arrangement of the above-noted type wherein the collector is provided with an end piece which projects into an expansion chamber which is centrally arranged in the housing.
The low exhaust back pressure is achieved by the central arrangement of the expansion chamber and the complete symmetrical acting upon the catalysts which follows.
The discharge of the exhaust gases flowing through the catalysts by way of separate exhausts also provides a symmetrical low exhaust back pressure. Furthermore, the central position of the expansion chamber permits a space-saving arrangement of this chamber and of the adjacent catalysts in a common housing. The exhaust gases can be guided to the catalytic emission control system by way of short pipes and lines. Thus, the catalysts rapidly reach their temperature required for an optimal emission control.
The flowing of the exhaust gases into the expansion chamber arranged centrally in the housing and the dividing into two separate exhaust gas flows that takes place there, which exhaust gas flows act directly, without any reduction of the cross-section, upon the main catalysts by way of large-surface perforated metal sheets, permits a fast parallel flowing through the main catalyst monoliths and the subsequent discharging of the purified exhaust gases by way of one separate exhaust respectively.
The low exhaust back pressure promotes a good power development of the internal-combustion engine while the fuel consumption is reduced at the same time. The arrangement of the housing transversely with respect to the longitudinal direction of the internal-combustion engine permits a symmetrical arrangement of the lines and offers a large space for the housing of the main catalysts. A large catalyst volume is the prerequisite for a long working life of the catalyst.
A damper volume surrounding the catalysts acts in a damping manner together with the expansion chamber arranged in front of the main catalysts which, on the one hand, results in acoustic advantages and, on the other hand, reduces pressure peaks in the exhaust gas flow which otherwise may result in damage to the catalysts or to the whole housing. The large volume of the exhaust system has a damping effect on pressure fluctuations.
According to the working volume of the internal-combustion engine and according to acoustic requirements, all exhaust pipes together may be guided in an exhaust collector into the expansion chamber or a separate collector may be assigned to one cylinder bank respectively.
For acoustic and fluidic reasons as well as because of the component strength, it was found to be advantageous to close the end pieces of the collector in the expansion chamber at the end and to let the exhaust gases flow out by way of openings on their lateral surface.
In order to meet also the strictest emission control regulations, starting catalysts may be inserted in the exhaust collector or collectors whose small monolith mass, because of the arrangement close to the combustion chamber, reaches its working temperature particularly fast.
These starting catalysts may have, for example, as switchable catalysts, ring-shaped monoliths which surround an at first closed central duct. After the working temperature of the main catalysts has been reached, the central duct is opened up so that the exhaust gas will no longer flow through the monoliths. For a particularly fast-acting emission control, a separate starting catalyst, which is inserted in the respective exhaust pipe, may be assigned to each individual cylinder of the internal-combustion engine.
In an advantageous development of the invention, the housing may be constructed in a double-walled manner as a heat exchanger and may be provided with connection pieces. By way of these connection pieces, the fresh air to be heated is supplied which is heated by the energy contained in the exhaust gases and is then, by way of additional connection pieces, supplied, for example, to the interior of a vehicle equipped with such an exhaust system.
For the control of the fuel-air mixture of the internal-combustion engine and for the monitoring of the operatability of the catalysts, several lambda probes are arranged in the exhaust system. The control of the mixture, in this case, is carried out by, in each case, one or two first lambda probes arranged upstream of the catalysts, while second or third probes arranged downstream of catalysts are used for the catalyst monitoring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.